There were a number of units I considered when constructing the rule (Flying MCs, Vehicles, Walkers). I simply thought it was easiest and was still relatively in line with the Troops-theme that pervades most missions.
If an all-bike list has to take a Land Speeder of outflanking Scouts to try and win the mission, I'm not saying that's a bad plan...
Do remember. Attackers can start 24" away from deployment and are guaranteed to go first. It should be a bloody good time!